1. Field of the Invention
This invention relates to a musical waveshape processing system for an electronic musical instrument in which time-division time slots are set corresponding to a plurality of channels and the musical waveshape amplitude value of each channel is repeatedly calculated to produce a note.
2. Description of the Prior Art
In recent years, there have been proposed a variety of electronic musical instruments employing digital techniques. Such electronic musical instruments are excellent in that a musical waveshape, an envelope waveshape and a frequency can be controlled easily at will, as compared with conventional electronic musical instruments using analog techniques. A digital circuit is suitable for fabrication as an integrated circuit, and hence provides for enhanced reliability and suited for reduction of the circuit scale. In the abovesaid electronic musical instruments, however, note producing channels are provided for the reduction of the circuit scale, the number of keys which can be simultaneously depressed for producing notes is limited to 10 to 15 but, in general, musical waveshape memories equal to (the number of tone systems).times.(the number of channels) are required for producing notes separately for respective tone systems, for example, flute, string, reed and like ones. However, the provision of some dozens of musical waveshape memories imposes a severe limitation on the reduction of the circuit scale. Recently, a peculiar digital organ has been proposed in which a waveshape amplitude value is calculated by inverse Fourier transformation in a time-divided time t.sub.x. The time t.sub.x is subdivided into 16 time slots and, in the respective time slots, first to sixteenth harmonics are calculated. With this method, the circuit structure used is much simplified as compared with the abovesaid method but it is necessary to raise the time-division frequency for further division of the time slot in each channel to the number of harmonics (for instance, 16). Accordingly, processing for the time-division frequency is complicated. The present inventors have found that since the above problem basically arises from the calculation method, if the calculation method using a function, which had already been proposed by the present applicants, is employed, processing can be achieved at a lower time-division frequency only by providing time-division time slots corresponding to a plurality of channels because the time slots need not be further divided, and that since a note can be produced directly be carrying out the musical waveshape calculation and envelope addition in synchronism with each of the time-division slots corresponding to the channels, the musical waveshape memory part can be simplified.